Induction heating cut-off means



Dec. 11, 1962 R. F. TAMM 3,068,336

INDUCTION HEATING CUT-OFF MEANS Filed Nov. 25, 1960 INVENTOR. Emumzo FTAMM "3 mfwzz, mg/mwzy ATTQQNEYS United States Patent ()fiicc 3,068,335Patented Dec. 11, 1962 3,068,336 INDUCTION HEATING CUTOFF MEANS RichardF. Tamm, Elmhurst, Ill., assignor to Continental Can Company, Inc., NewYork, N.Y., a corporation of New York Filed Nov. 23, 1960, Ser. No.71,348 19 Claims. (Cl. 219-75) This invention relates in general to newand useful improvements in the can making art, and more particularlyrelates to novel means for severing connecting tabs extending betweenand connecting together adjacent can bodies.

It has been proposed to form can bodies by first providing the desiredmetal stock in strip form, which metal stock is then welded into anelongated tube. After the tube has been formed, the tube is broken apartat pre determined intervals along score lines which normally are formedin the stock prior to the forming of the tube therefrom. The individualcan bodies are not completely broken apart in that they remain connectedtogether by connecting tabs extending along the line of the welded seam.In the formation of can bodies, it is necessary that these connectingtabs be completely removed without the removal of an excessive amount ofthe end of a can body. It is to this that the present invention relates.

. The present invention proposes to separate can bodies or other tubularmembers which are connected together by connecting tabs by electricallyheating the connecting tabs to effect the melting thereof. Whileelectrical current may be introduced into the connecting tabs by directcontact of electrodes with the surface of the can bodies, it has beenfound convenient in the formation of the tube to provide a protectivelacquer coating at least over the Welded seam, such lacquer coatingbeing required in the finished can. As a result, it is not feasible toattempt to pass the necessary electrical current through the connectingtabs utilizing direct contacting electrodes.

' In view of the foregoing, it is the primary object of this inventionto provide a novel method of attaining separation of two conductivebodies joined by a restrictive conductive bridge, which method includesthe applying of alternating magnetic field effects to the bridge therebyinducing an electric current flow in the bridge of such intensity thatthe material of the bridge is either melted .or is raised to atemperature at which the bridge is physically weakened, after which thebodies may be pulled apart, and the heating effect being primarilyrestricted to the bridge with the heating of the bodies beinginsuflicient to have any detrimental effects on either the material ofthe bodies or coating which may be disposed on the bodies.

Another object of this invention is to provide an induction heatingcoil, which coil is specifically shaped so as to generally permit thepassage of can bodies and other interconnected tubular members adjacentthereto and to concentrate the flow of electrical current in the canbodies in the connecting tabs extending between and connecting togetheradjacent can bodies so that the connecting tabs may be rapidly heated tothe temperature necessary to effect the melting thereof with a minimumexpenditure of electrical energy and a minimum heating of the can bodiesadjacent the connecting tabs.

' Another object of the invention is to provide a novel apparatus forsevering connecting tabs between tubular members, such as can bodies,the apparatus including means for feeding and guiding the tubularmembers with adjacent ends of adjacent tubular members being spacedapart and being connected together only by the connecting tabs, andthere being disposed along the path of the tubular members an inductionheating coil, which induction heating coil functions to concentrateelectrical current in the connecting tabs as they pass adjacent theinduction heating coil to effect the rapid heating and melting of theconnecting tabs.

Still another object of the invention is to provide a novel inductionheating coil for effecting the electrical heating and melting ofconnecting tabs extending between tubular members, such as can bodies,the induction heating coil having two elongated legs connected togetherby an arcuate intermediate interconnecting portion to permit tubularmembers to pass between the legs, and the legs being provided withintermediate portions of a generally V-shaped outline which are alsoarcuate in transverse section so as to concentrate the flow ofelectrical current in the tubular members in the area of the connectingtabs therebetween so that the heating of the tubular members isprimarily limited to the connecting tabs.

A further object of the invention is to provide a novel method ofsevering connecting tabs between adjacent tubular members, the tubularmembers being in the form of can bodies and the like, the methodincluding the steps of passing the tubular members along a predeterminedpath with opposed ends of adjacent tubular members being spaced apartand disposed in angular relation and the tubular members being connectedtogether only by connecting tabs extending therebetween, and passing theso arranged tubular members through an induction heating coil to efiectthe concentrated flow of electrical current through the connecting tabswith the electrical current rapidly heating and effecting the melting ofthe connecting tabs.

Still another object of the invention is to provide a novel apparatusfor severing connecting tabs between ad'- jacent tubular members, theapparatus including suitable feed and guide means for feeding thetubular members along a predetermined path with the feed and guide meansincluding means for tensioning the connecting tabs between adjacenttubular members, and there being provided induction heating means foreffecting the concentrated flow of electrical current through theconnecting tabs at such time as the tabs are tensioned whereby the tabsmay be rapidly heated through the concentrated flow of electricalcurrent to a temperature where the tabs are physically weakened, afterwhich the tension applied thereto will be sufiicient to pull the tubularmembers apart.

With the above, and other objects in view that will hereinafter appear,the nature of the invention will be more clearly understood by referenceto the following detailed description, the appended claims, the severalviews illustrated in the accompanying drawing:

In the drawing:

FIGURE 1 is a schematic elevational view showing generally the detailsof the apparatus provided for the induction heating of the connectingtabs between tubular members in accordance with the invention.

FIGURE 2 is an enlarged fragmentary plan view, showing the specificrelationship of the induction heating coil, two tubular members and theconnecting tab therebetween, the view showing the concentration ofelectrical current within the connecting tab.

FIGURE 3 is an enlarged fragmentary elevational view similar to FIGURE2, and shows further the rela-= tionship of the induction heating coil,the two tubular members and the connecting tab, as well as the flow ofelectrical current through the connecting tab.

FIGURE 4 is a perspective view of the induction heating coil, and showsthe specific configuration thereof.

In accordance with the invention, an elongated tube is formed having awelded seam. The tube is then partially broken at predeterminedintervals along score lines to define individual tubular members whichmay be in the form of can bodies and will be so referred to hereinafter.The can bodies are referred to by the letter B and are connectedtogether by connecting tabs T which are disposed along the welded seamS.

After the can bodies B have been partially broken apart, they aresuitably guided so that adjacent ends of adjacent can bodies are inspaced relation and the can bodies are connected together only by theconnecting tabs T. While this may be accomplished in many ways, one ofthe easiest ways of accomplishing this is to pass the can bodies B aboutan arcuate path. For illustrative purposes, the can bodies B are passedthrough a plurality of sets of guide rollers 5, 6, 7 and 8. Each set ofguide rollers includes at least two guide rollers disposed in opposedrelation, and it is preferred that the guide rollers be generally of anhourglass shape so as to at least partially confine the can bodies B.Further, it is preferred that at least one set of the guide rollers 5, 6and 7 be driven, and that the guide rollers 8 be driven so as to removethe separated can bodies B. It may also be desirable to drive the guiderollers 7 and 8 at different speeds so as to apply a tensile stress inthe connecting tabs T during the heating thereof.

The apparatus of this inventionalso includes an induction heating coil Cwhich is formed in accordance with the following principles. aremagnetically linked, analternating current flowing in onecircuit willinduce a current in the other. The magnitude of the induced current isproportional to the magnitude of the primarycurrent, the frequency, theratio of the number of turns in the two circuits, and the degree towhich thetwo circuitsare magnetically interlinked. If a single turn coilis positioned closely parallel to a conducting plane, such as a thinsheet of metal, a current will be induced in the sheet. The magnitude ofthis current. is. a function of the primary current, the currentfrequency and varies inversely with the distance between the coil andthe metal sheet. This induced current produces 1 R heat; hence, thegreater the current density, the greater the rate of heat generation.

At frequencies used in radio frequency induction heating, the currenttakes the path of least impedance and concentrates in a section of themetal which is directly in line with, and follows as closely aspossible, the path of the primary current in the coil. At the higherfrequencies, the skin effect becomes important. This effect manifestsitself in a tendency for the current to concentrate closer to thesurface of the conductor as the frequency is increased.

As set forth above, the induced current magnitude is a function of coilproximity to the surface; i.e., the smaller the distance, the greaterthe current. The current density varies in a similar manner; i.e., atsmall distances, the general outline of the induced current will conformmore closely to the outline of the induction coil, and therefore theheat effect will be more concentrated. For example, if a coil having thegeneral outline of a dumbbell is held close to a conducting surface, theinduced current and heat zone will have a similar shape. As the coil ismoved away from the conducting surface, the dumbbell shape of theinduced current degenerates into two circles of more diffuse outline,and the heated area will have a similar shape.

For the problem of can body separation from broken, welded, prescoredtubing moving continuously past a stationary, continuously energizedinduction coil, one may choose to induce a dumbbell-shaped current inthe tubular members with the narrow waist area of the current beingcentered over the welded seam to produce maximum heating effect alongthe seam. Such a current shape and resultant heat Zone can be achievedwith a coil of the general shape of the illustrated induction heatingcoil C. The induction heating coil C is formed of a pair of generallyparallel legs 9 which are connected together by an intermediateconnecting portion 10. Each of the legs 9 includes an elongated rearportion 11, an

When two electrical circuits offset intermediate portion 12 which isgenerally V-shaped in outline, and a forward portion 13, the forwardportion 13 being disposed at a slight angle to the rear portion 11. Eachforward portion 13 terminates in an upwardly slop ing portion 14 which,in turn, is connected to the connecting portion 10.

It is to be noted that the connecting portion 10 is arcuate intransverse section so that it arches up and over can bodies B passingbetween the legs 9 Also, it is to be noted that the V-shapedintermediate portions 12 are disposed in opposed relation with theapices thereof spaced apart and that the V-shaped intermediate portions12 are arcuate in transverse cross-section so as to conform generally tothe arcuate cross-section of the can bodies B.

The required amount of electrical energy is supplied to the inductionheating coil C by a transformer, generally referred to by the numeral15. The transformer 15 includes a primary winding 16 which is connectedby wires 17, 18 to a suitable power source. The transformer 15 alsoincludes a secondary winding 19 which is 6011f nected to one of the legs9 by a wire 20. The other end of the secondary winding 19 may bedirectly connected to the other of the legs 9, or may be connected to acontrol device 21 by means of a wire 22. The control device 21 is thenconnectedto the other of the legs 9 by a wire 23. The control device 21may be of any suitable type which will detect the spacing betweenadjacent can bodies B and the positioning of a connecting tab T withrespect thereto. and thus pulse the flow of electrical current to theinduction heating coil C in timed relation to the passage of theconnecting tabs T therethrough.

It will be noted from FIGURES 2 and 3 in particular that theintermediate V-shaped portions 12 of the induction heating coil-Cconverge generally towards the path of the connecting tabs T. The apicesof the V-shapcd portions 12 approach the can bodies B more closely thanthe other portions of the induction heating coil C, which, althoughtending in general to conform to the curved shape of the can bodies B,gradually recede from the surfaces thereof in order to render theheating effect more diffuse. The final position of the induction heatingcoil C and its current level are so chosen that the heat produced in thewelded seam area of the can bodies B is below a level that would damagethe metal or a coating which may be thereon when the can bodies B arewithin the influence of the induction heating coil C. However, when aconnecting tab T is centered under the induction heating coil C, thecurrent path for the dumbbell waist of the induced current is suddenlygreatly restricted by the narrow width of the connecting tab T, thecurrent density and heating effect is greatly magnified, and theconnecting tab area rapidly reaches softening or melting temperaturelevels.

The flow of electrical current through the connecting tabs T issufficient to heat the connecting tabs T to a melting temperature topermit the rapid melting and parting of the connecting tabs T. Aspointed out above, if desired, the rollers 7 and 8 may differentially bedriven so as to produce a tension in the connecting tabs T and thus theseparation of the can bodies B can be a function of heating and tensilestress. However, the severing of the connecting tabs T may beaccomplished by heating and melting alone. It is also pointed out thatthe current flow may be pulsed utilizing a control device, such as thecontrol device 21, so that the flow of induced current is T is disposedgenerally between the V-shaped portions limited primarily to that timeat which a connecting tab 12 of the induction heating coil C.

Although the induction heating coil C illustrated and described hereinis a desirable form of induction heating coil to be used in accordancewith this invention, it is to be understood that other shapes ofinduction heating coils could be utilized in accordance with theinvention. For example in a timed, pulsed operation, it may be moreadvantageous to devise a coil shape which produces an intensely heatedarea of small dimension centered at the tab location such as a smalldiameter solenoid or a conically-shaped solenoid.

- It will be readily apparent from the foregoing description of theapparatus and operation thereof that direct electrical contact with themetal of the can bodies is not required. Accordingly, can bodies andother tubular members, either having exposed metal or coated, may bereadily separated utilizing the apparatus.

From the foregoing, it will be seen that novel and advantageousprovision has been made for carrying out the desired end. However,attention is directed to the fact that variations may be made in theexample method and apparatus disclosed herein without departing from thespirit and scope of the invention, as defined in the appended claims.

I claim:

1. An apparatus for severing selected connecting tabs between adjacentconductive metal bodies comprising feed and guide means for movingbodies along a predetermined path, and an alternating-current-carryingconductive loop having first and second serially-connected branchesconfigured and disposed symmetrically with re spect to the path ofmotion of said tabs, said first and second branches respectivelycomprising an intermediate portion disposed substantially parallel to anedge portion of one of said bodies, thence substantially parallel to andclosely spaced apart from the proximate connecting edge of said tab, andthence parallel to the adjacent edge portion of a next proximate one ofsaid bodies, whereby a maximum concentration of induced current in theconnecting tabs is elfected for the heating of said tabs.

2. The apparatus of claim 1 wherein said feed and guide means includestwo sets of feed members disposed on opposite sides of said inductionheating means for driving adjacent bodies at different rates to thustension the connecting tabs therebetween and assist in the separation ofthe bodies.

3. An apparatus for severing selected connecting tabs between tubularmembers comprising feed and guide means for moving the tubular membersin a predetermined path with adjacent ends of the tubular members spacedapart and disposed in angular relation and the tubular members beingconnected together by connecting tabs disposed at the apices of anglesbetween the tubular members, and means positioned along said path forinducing heating current into the tubular members and for producing amaximum concentration of current in the selected connecting tabs toeffect the concentrated heating of the selected connecting tabs, saidmeans including a specially shaped induction heating coil.

4. The apparatus of claim 3 wherein said feed and guide means includestwo sets of feed members disposed on opposite sides of said inductionheating means for driving adjacent bodies at different rates to thustension the connecting tabs therebetween and assist in the separation ofthe bodies.

5. The apparatus of claim 3 wherein said induction heating coil extendsgenerally longitudinally of the path of the tubular member and hasopposed intermediate portions for effecting the concentration of currentin the tabs.

6. The apparatus of claim 3 wherein said induction heating coil has apair of legs extending generally longitudinally of the path of thetubular members on opposite sides thereof, and an intermediateconnecting portion, said legs having intermediate opposed portionsdirected generally towards the path of the connecting tabs for effectingthe concentration of current in the tabs.

7, The apparatus of claim 3 wherein said induction heating coil has apair of legs extending generally longitudinally of the path of thetubular members on opposite sides thereof, and an intermediateconnecting portion, said legs having intermediate opposed portionsdirected generally towards the path of the connecting tabs for efiectingthe concentration of current in the tabs, said intermediate connectingportion and said leg portions being generally arcuate in elevation andclosely following the outlines of the tubular members.

' 8. The apparatus of claim 3 wherein said induction heating coil has apair of legs extending generally longitudinally of the path of thetubular members on opposite sides thereof, and an intermediateconnecting portion, said legs having intermediate opposed portionsdirected generally towards the path of the connecting tabs for effectingthe concentration of current in the tabs, said intermediate opposedportions being generally V-shaped.

9. The apparatus of claim 3 wherein said induction heating coil has apair of legs extending generally longitudinally of the path of thetubular members on opposite sides thereof, and an intermediateconnecting portion, said legs having intermediate opposed portionsdirected generally towards the path of the connecting tabs for effectingthe concentration of current in the tabs, said intermediate connectingportion and said leg portions being generally arcuate in elevation andclosely following the outlines of the tubular members, said intermediateopposed portions being generally V-shaped.

10. The apparatus of claim 3 together with means for controlling theflow of current through said induction heating coil in timed relation tothe movement of the tubular members.

11. A method of attaining separation of two conductive metal bodiesjoined by a restrictive conductive bridge with a surface extending fromone body across the bridge and onto the other body, which comprisesinducing in each body at areas thereof adjacent the bridge eddy currenteffects with like magnetic polarity at said surface, whereby theintersection of the eddy currents causes current flow from one inductionarea to the other and back to thereby heat and weaken the bridge, andthen pulling the bodies apart.

12. A method of attaining separation of two conductive metal bodiesjoined by a restrictive conductive bridge with a surface extending fromone body across the bridge and onto the other body, which comprisesmoving the bodies, inducing in each moving body at areas thereofadjacent the bridge eddy current effects with like magnetic polarity atsaid surface, whereby the intersection of the eddy currents causescurrent flow from one induction area to the other and back to therebyheat and weaken the bridge.

13. A method of attaining separation of two conductive metal bodiesjoined by a restrictive conductive bridge with a surface extending fromone body across the bridge and onto the other body, which comprisesmoving the bodies, inducing in each moving body at areas thereofadjacent the bridge eddy current effects with like magnetic polarity atsaid surface, whereby the intersection of the eddy currents causescurrent flow from one induction area to the other and back to therebyheat and melt the bridge.

14. The method of attaining separation of two conductive bodies joinedby a restrictive conductive bridge, which method comprises applyingalternating magnetic field efiects to the bridge thereby inducing anelectric current flow in the bridge of such intensity that the materialof the bridge is raised to a temperature at which the bridge isphysically weakened, and then pulling the bodies apart.

15. A method of severing connecting tabs extending between andconnecting together adjacent tubular members, the method comprising thesteps of disposing adjacent tubular members at small angles to eachother with the tubular members being out of engagement with one anotherexcept for the connecting tabs, and passing the tubular members throughan induction heating coil and concentrating current flow in theconnecting tabs to efl'ect the heating and melting of the connectingtabs.

16. The method of claim 15 wherein the fiow of current through theinduction heating coil andthe tubular members is timed in relation tothe movement of the tubular members to limit current fiow in the tubularmembers to the general areas of the connecting tabs.

17. An induction heating coil for severing connecting tabs extendingbetween and connecting together tubular members, said induction heatingcoil comprising a pair of elongated legs disposed generally in parallelrelation, and an intermediate connecting portion, said legs havingintermediate portions of a generally V-shaped outline disposed inopposed relation.

18. The induction heating coil of claim 17 wherein said connectingportion and said opposed portions of the legs are arcuate in transversesection to permit the passage of tubular members generally within theconfines of the induction heating coil.

19. An apparatus for severing selected connecting tabs between tubularmembers comprising feed and guide means for moving the tubular membersin a predetermined path With adjacent ends of the tubular members spacedapart and disposed in angular relation and the tubular members beingconnected together by connecting tabs disposed at the apices of anglesbetween the tubular members and an a1ternating-current-carryingconductive loop having first and second serially-connected branchesconfigured and disposed symmetrically with respect to the path of motionof said tabs, said first and second branches respectively comprising anintermediate portion disposed substantially parallel to an edge portionof one of said bodies, thence substantially parallel to and closelyspaced apart from the proximate connecting edge of said tab, and thenceparallel to the adjacent edge portion of a next proximate one of saidbodies, whereby a maximum concentration of induced current in theconnecting tabs is effected for the heating of said tabs.

References Cited in the file of this patent UNITED STATES PATENTS2,187,740 Hothersall Jan. 23, 1940 2,467,201 Frazier Apr. 12, 19492,507,817 Rapp et al May 16, 1950 2,512,893 Gahr June 27, 1950 2,599,229Bukaty June 3, 1952 2,655,588 Wadhams Oct. 13, 1953 2,716,693 WadhamsAug. 30, 1955

